# Why is it safer to place a switch on the positive side of a voltage source?

According to the research I've done, it is safer to place a switch on the positive side of a voltage source:

This only makes sense to me visualizing the circuit using conventional current (counter clockwise). When visualizing it in electron flow (clockwise), the opposite seems true. I think this stems from my use of the "water analogy."

Why does a switch go on the positive side of a voltage source?

In theory there is no difference, but practically there is because of how most engineers use "ground".

The problem is how sure are you that you truely are opening all paths for electricity to flow? If "circuit ground" is tied to the actual ground, something which happens to be resting on the ground may form a closed loop.

simulate this circuit – Schematic created using CircuitLab

This is common in "mains" electricity (i.e. the wall outlets), so if SW1 is closed, Joe is having a bad day. SW2 doesn't matter, and it doesn't matter if V1 is positive or negative.

Another common example is when you connect "ground" to a metallic chassis, which is common in the automotive world. The circuit for this looks similar to the one above. If you want to use a low-side switch, you had better make sure you don't have any metal contact with the body of the car or anything electrically connected to the body.

• I wonder if there’s implications for reduced arcing if any. Feb 24 at 18:45

Usually the negative terminal of the voltage source is considered Zero Volts, or Ground. In that case, the switch in the positive feed will remove all power from the load. If the switch was in the negative side, the load would still have power applied, and an accidental ground somewhere could cause unpleasant surprises, as motors start, lights flash....

A more general description of the preferred switch location is "in the ungrounded supply line, as close to the power source as practical". This covers AC power and positive ground circuits as well as negative ground.

• Imagining a real-world circuit, is a battery the same as the voltage source (in orientation as well)? Dec 24, 2015 at 1:07

The circuit works the same no matter where you put the switch. Part of the electrical code (for house wiring) says that the switch should always go between the hot conductor and the load. This is for safety. Since the neutral (white wire) is referenced to ground, it should not have any potential relative to someone touching it. If the switch was placed to break the circuit on the neutral wire, it would mean that there is potential on a plugged in device and some length of neutral wire up to the switch even when it is turned off. This is potentially dangerous because an unsuspecting person might touch a white wire thinking it is neutral. In this case it would actually be hot. It's an extra layer of safety so you know that white wires are never hot, although you should still never touch live wiring.